What about reports in the news of people recovering but then getting reinfected after a short period of time?

These are important questions that I have been getting quite often from my patients, friends, family, neighbors, and even total strangers. I answered it in a previous post but because of the number of questions wanted to update the topic. Many people have become infected with COVID-19 and recovered and are concerned that they may get infected again. There are really two questions: ‘Are you immune if you have recovered from COVID-19?’ and ‘How long does the immunity last?’.

Can you get reinfected?

News reports from China and Japan have indicated that some patients with COVID-19 who were discharged from the hospital after a negative coronavirus test were readmitted to the hospital again and this time tested positive. More recently there have been reports from Korea of patients becoming “reinfected”. On the surface this seems to suggest that you can get the infection again. This is how this information is portrayed in the news leading to great anxiety but that anxiety is probably unnecessary.

The first thing to note is that it is possible that there were inaccurate test results somewhere along their disease course. In most places a patient is deemed fully recovered when two tests conducted with a 24-hour interval show negative results but there are a high number of false negative tests. If this is the case a patient can be incorrectly classified as having cleared the infection and discharged. The repeat test on readmission is then not a new infection but a remnant of clearance of the original infection. Second is that, when they are readmitted and have a positive test it does not mean that that test indicates that the virus is active. Remember a positive test for the virus does not always mean that the virus is active. There has been research showing that even though viral testing is positive for several days in people who have recovered there is no viral replication. If there is no viral replication there is no infection and the person is not contagious. In other words, the positive tests are only detecting “dead” virus RNA.

So here’s the one possible scenario leading to these cases of ‘reinfection’:

A person gets sick and tests positive for COVID-19.

They recover and some will have 2 falsely negative tests that allow them to be discharged.

They then get a cough from allergies, a common cold, asthma, etc and go back to the hospital.

They get another test which is positive but is residual virus from their first infection and not indicative of active disease.

Here’s another possibility:

A person gets sick with influenza or another respiratory virus (they have not gone on vacation just because COVID-19 is getting all the press).

The have a false positive test and are presumed to have COVID-19.

They recover from their non-COVID infection and are sent home.

They then get a true COVID-19 infection and test positive.

There is the possibility of viral reactivation which would be concerning but because of the above issues with testing accuracy it is not clear if the reported cases were true reactivations. There are many questions that still need to be answered from the Korean data (which has yet to be analyzed and published). It was not reported if these patients were symptomatic, if so how symptomatic, how soon after being “cleared” were they retested, or if they were shedding live virus vs having only positive viral gene testing.

Even with all that it is possible that, if someone develops a mild case, they do not have a robust enough of an immune response to confer resistance to reinfection. Even if reinfection were somehow possible it is likely to result in a much milder infection which is shorter lived and less contagious. I am personally not worried about reinfection or reactivation for the health of the individual but it may become a public health issue.

There are many reasons to believe that coronaviruses do not cause reinfection. For this particular coronavirus, a study that included 82 confirmed and 58 probable cases of COVID-19 from China showed the presence of neutralizing antibodies 10-18 days after symptom onset. There is also evidence showing that recovery from all other coronavirus infections leads to immunity lasting many months or years after the original infection. There is evidence from primates that infected monkeys do not become reinfected after being exposed to the virus a second time. While the evidence on reinfection is evolving, current data and experience from other viruses (without substantial seasonal mutation like flu) show that reinfection does not happen in the short term.

How long are you immune?

Even though you are likely to be immune after infection it may be only a short period of time. This obviously raises the question of how long. This is a bit more complicated of a question. Because the outbreak is only a few months old, there are no data on long term immune response.

For some viruses, like measles and polio, protective antibodies are around for your entire life, but for others it’s not so long. For some infections like tetanus you need a regular “booster” to prolong the immune response. Some viruses, like the flu, mutate and you need a new vaccine every year. The bottom line is, that not all infections are the same in this regard.

Coronaviruses come in different flavors. There are the mild ones that cause the common cold. Immunity to these coronaviruses last only about 1-3 years. The severe coronavirus that is afflicting us now is more like the one that caused SARS outbreak in 2003. That one was named SARS-CoV-1 and this one SARS-CoV-2 because they are similar in many ways. Data from SARS-CoV-1 indicate that titers of IgG and neutralizing antibodies peaked at 4 months after infection, with a subsequent decline through at least 3 years after infection.

Bottom Line

Currently there is no good evidence that one can become reinfected in the short term after recovery but recovery and immunity need to be documented somehow. There is good evidence from other similar coronaviruses to support the fact that immunity lasts for at least several months but possibly several years. There is a lot that needs to be sorted out in the coming weeks and months but data is constantly being collected sorting these issues out.

These questions should be answered relatively soon as the data from the early infections in other parts of the world comes out and as data from antibody and vaccine studies becomes available, For now we must still assume we are at risk for the benefit of the public health.

For my opinion on how this information could lead to a way out of this crisis read this.

Hopefully we, and you, will get the answers about how long immunity lasts. Your analysis seems spot on to me, and it illustrates why everyone needs to be very careful in interpreting case reports–they are no substitute for studies and other epidemiological data. I have followed the statistics from the Pennsylvania Department of Health on a daily basis. There have been 24,199 diagnosed cases in PA; less than 1% of them have been in children 12 and under. Of the 2231 hospitalizations reported, less than 3% have been people 24 and under. I find it hard to believe that children are not exposed at the same rate as adults. Why do you think that children overwhelmingly seem to be so resistant to this disease?

It appears that their immune systems are not developed enough to develop a massive response to the virus. Alternatively, there may be differences in expression of the ACE receptors that are necessary for viral entry.